Prior art products for melting snow and ice include hygroscopic salts such as calcium chloride and magnesium chloride, rock salt (sodium chloride), fertilizers such as potassium chloride and urea, mixtures of these various salts, and non-slip aggregates such as sand, cinders and calcined diatomaceous earth absorbents.
These prior art products, which are incapable of melting snow and ice in their solid form, must first form a liquid solution or brine. The brine serves to lower the freezing point of water and to dissolve or melt snow and ice on contact, until such time that it becomes diluted to a concentration where its freezing point is raised near that of water.
As will be readily appreciated by those skilled in the art, the speed or effectiveness of these prior art products depends, in part, on the time needed for a brine to form. In order to reduce the brine conversion time, hygroscopic salts (e.g., calcium chloride, magnesium chloride) have been combined with e.g. sodium chloride and/or potassium chloride and urea. These prior art salt blends have been prepared as dry blends and as agglomerates. These blends have also been prepared by spraying a liquid solution of calcium chloride and/or magnesium chloride onto sodium chloride crystals.
Dry salt blends comprising calcium chloride and sodium chloride tend to be the least effective salt blend products due to the separation of these components during shipping. As is well known, calcium chloride has a strong exothermic heat of dissolution while sodium chloride has an endothermic heat of dissolution. As such, dissolution of sodium chloride will occur only with absorption of heat and is therefore dependant upon the heat released by the dissolution of calcium chloride. If these components are not in direct contact, then the sodium chloride dissolution rate is lowered rendering the blend less effective.
The coated sodium chloride crystals and salt blend agglomerates noted above, typically do not contain sufficient quantities of calcium chloride and/or magnesium chloride to achieve acceptable dissolution rates, or to effect complete dissolution of the sodium chloride crystals.
Included among the prior art attempts to improve upon the effectiveness of existing snow and ice-melting products was a granulated product prepared from a compacted 50/50 blend of calcium chloride and sodium chloride. The blend was reportedly prepared using anhydrous calcium chloride pellets (94% CaCl2//4% other salts//2% H2O) and 100 mesh sodium chloride particles (92% of NaCl//8% of a 38% by weight (wt.), CaCl2 solution). The total amount of free water in the anhydrous calcium chloride pellets and calcium chloride solution was 2%.
While this granulated product contained sufficient quantities of calcium chloride to effect dissolution of the sodium chloride component at acceptable dissolution rates, it was expensive to manufacture and was readily reduced to a powder when subjected to mechanical loadings during transit and storage.
Accordingly, it is a primary object of the present invention to address the above-referenced disadvantages of the prior art.
More particularly, it is an object of the present invention to provide snow and ice-melting granules that have improved mechanical properties, yet are less expensive to manufacture.
It is another object of the present invention to provide a method for preparing snow and ice-melting granules that is efficient and economical and that serves to effect an increase in the mechanical properties of the final granule composition.
It is yet a further object of the present invention to provide granules prepared in accordance with the method described herein.